The best Coincidence Time Resolution (CTR) obtained so far – with very short crystals of 3–5mm in length – reach values between 100 and 150ps. Such crystals are not really practical for a TOF PET ...imaging device, since the sensitivity is quite small for the detection of the 511keV gammas resulting from a positron annihilation. We present our setup and measurements using 15mm length crystals; a length we regard as reasonable for a TOF-PET scanner. We have used a new series of Silicon Photo-Multipliers (SiPM) manufactured by Hamamatsu. These are the High Fill Factor (HFF) and Low Cross-Talk (LCT) Multi-Pixel Photon Counters (MPPC). We have compared three different crystals, LFS-3 (supplied by Zecotek) and two samples of LYSO (manufactured by Saint Gobain and CPI). We have obtained an excellent value of 148 ps for the Coincidence Time Resolution (CTR) with two LFS-3 crystals (15mm long) mounted on each side of a 22Na radioactive source with the HFF-MPPCs at 3.3V over-voltage. Our results are148ps obtained with LFS-3 and 170ps with LYSO crystals using identical SiPMs and electronics.
The Multigap Resistive Plate Chamber (MRPC) is a gaseous detector that has low building costs and excellent timing performances. It is usually operated using a mixture of C2F4H2 and SF6, which have ...very high Global Warming Potential (GWP) values (1430 and 23,900 respectively). The ecological HFO-1234ze (C3F4H2), GWP <7, was investigated if it could be a viable alternative to the standard gas mixture. In this work, we present the performances of an MRPC with 10 gaps of 235μm width, built using 0.5 mm thick plates of low resistive glass. This detector was also operated using the standard gas mixture for comparison. At low particle rate, this detector reaches an efficiency of 98% and a time resolution of around 70 ps for the two mixtures of gases. We observed no degradation of its performances when a limited size of its active area is exposed to particle rates up to 63 kHz/cm2.
Two Multigap Resistive Plate Chambers (MRPCs) were built with thin (0.4 mm) low-resistive glass sheets for the inner plates and standard 0.28 mm ‘soda lime’ float glass as external plates. The 6-gap ...MRPC reaches 96.5% efficiency at 15.6 kV and a time resolution of 68 ps at an instantaneous particle flux around 2.5 kHz/cm2. The 20-gap MRPC reaches 98% efficiency at 18.8 kV and a time resolution of 32 ps. Compared to a 6-gap MRPC built previously with all plates made with soda-lime float glass, the two MRPCs made with low-resistive inner glass show a much higher count rate capability. A third MRPC with all plates made from low-resistive glass was also constructed to verify the operation at high particle flux. In this paper a relative rate capability comparison between the MRPCs has been performed under a pulsed beam with a small spot on the chamber. Their rate capability under full illumination with continuous particle flux needs to be further studied.
This paper reports on the results of time resolution measurements of Multigap Resistive Plate Chamber (MRPC). Three 20 gas gaps MRPCs were built with thin float glass sheets and different gap sizes: ...160μm, 140μm and 120μm. These chambers have been tested using a different gas flow configurations. The measurements indicate that to reach a better time resolution for small gap size (140μm and 120μm), a smaller gas volume of the chamber is preferable. The efficiency of the chambers in both gas flow configurations has been tested. A time resolution of 25 ps comprehensive of the front-end electronics jitter, with an efficiency of 98% has been achieved for the MRPC with 140μm gas gaps; this is the best time resolution. Moreover, all the chambers have been tested for different particle flux. At the highest particle flux tested, a time resolution better than 60 ps together with an efficiency higher than 80% has been achieved for all the detectors at an instantaneous particle flux of 30 kHz∕cm2. From the efficiency and time resolution study, the rate capability for these three MRPC is similar.
The Multigap Resistive Plate Chamber (MRPC) is a possible candidate for the Semi-Digital Hadronic Calorimeter (SDHCAL). Two 4.5×20cm2 active area MRPCs have been built to study the time resolution ...using the NINO ASIC as front-end electronics. The granularity of the active area is provided by a 4 × 16 array of 1×1cm2 pick-up pads. Two different designs have been used for the two chambers: a six gas gap MRPC (6-gap MRPC) with a 220μm gap size and a ten gas gap MRPC (10-gap MRPC) with a 160μm gap size. An efficiency of 95% and 97% has been reached respectively. A time resolution of 50 ps for the 6-gap MRPC and 30 ps for the 10-gap MRPC has been achieved. The multiplicity study of this two MRPCs shows that a large fraction of the single hit is recorded in the events (71% for 6-gap MRPC and 64% for 10-gap MRPC).
A 20 gas gaps multigap resistive plate chamber (MRPC) was built with thin (0.28 mm) glass sheets and 0.16 mm gas gap size. This chamber reaches 97% efficiency at 18.4 kV and a time resolution of ...32 ps (sigma) at an instantaneous particle flux around 2.5 kHz/cm2. Compared to a 6 gaps MRPC with 0.22 mm gas gap, this 20-gap MRPC shows a higher rate capability and much better time resolution. The efficiencies of the 20-gap MRPC reach 95%, 93% and 88% at instantaneous fluxes of 10 kHz/cm2, 14.5 kHz/cm2 and 20 kHz/cm2, respectively. The efficiencies of the 6-gap MRPC at the same flux are 90%, 85% and 77%. The time resolution of 20-gap MRPC degrades with the increase of particle flux. However, a time resolution of 39 ps was obtained at an instantaneous flux of 10 kHz/cm2.
Various experiments are searching for detectors that can cover large areas (as in the present LHC experiments) with excellent timing performances and insensitivity to magnetic field. A detector based ...on scintillators coupled to SiPM can fulfil these requirements. SiPMs are indeed replacing the standard PhotoMultiplier technology thanks to the many advantages, with the corresponding possibility to achieve also higher segmentations in calorimetry or other applications. Also in view of future colliders experiments like HL-LHC or FCC or medical applications like TOF-PET, an important R&D on timing performances of SiPMs-scintillator detectors has begun, with the goal of including them in the list of possible 4-D tracking-timing devices.
An R&D on SiPM coupled to scintillator time resolution has been performed in a cosmic ray setup. Different kind of SiPMs, geometries of SiPMs coupled to the scintillator and different size of scintillator have been also studied. A time resolution of ∼69 ps, comprehensive of the full electronic chain, from the front-end to the readout electronics, has been achieved with SiPMs coupled to a 2x2x3 cm3 plastic scintillator.
We report the results of three MRPC detectors built with soda lime glass and tested in the T10 beam line at CERN. The detectors consist of a stack of 280μm thick glass sheets with 6 gaps of 220μm. We ...built two identical MRPCs, except one had the edges of glass treated with resistive paint. A third detector was built with one HV electrode painted as strips. The detectors' efficiency and time resolution were studied at different particle flux in a pulsed beam environment. The results do not show any improvement with the painted edge technique at higher particle flux. We heated the MRPCs up to 40°C to evaluate the influence of temperature in the rate capability. Results from this warming has indicated an improvement on the rate capability. The dark count rates show a significant dependence with the temperature.
Over the last decade there have been commercial TOF-PET scanners constructed using Photo-Multiplier Tubes (PMT) that have achieved ~500ps FWHM Coincidence Time Resolution (CTR). A new device known as ...the Silicon PhotoMultiplier (SiPM) has the potential to overcome some of the limitations of the PMT. Therefore implementing a SiPM based TOF-PET scanner is of high interest. Recently Philips has introduced a TOF-PET scanner that uses digital Silicon PhotoMultipliers (d-SiPMs) which has a CTR of 350ps. Here we will report on the timing performance of two Hamamatsu 3×3mm2 analogue-SiPMs read out with the NINO ASIC: this is an ultra-fast amplifier/discriminator with a differential architecture. The differential architecture is very important since the single-ended readout uses the ground as the signal return; as the ground is also the reference level for the discriminators, the result is high crosstalk and degraded time resolution. However differential readout allows the scaling up from a single cell to a multi-cell device with no loss of time resolution; this becomes increasingly important for the highly segmented detectors that are being built today, both for particle and for medical instrumentation.
We obtained excellent results for both the Single Photon Time Resolution (SPTR) and for the CTR using a LYSO crystal of 15mm length. Such a crystal length has sufficient detection efficiency for 511keV gammas to make an excellent PET device. The results presented here are proof that a TOF-PET detector with a CTR of 175ps is indeed possible. This is the first step that defines the starting point of our SuperNINO project.
PDF
